I'm new new on boating fishing too, I had a boat for few years & using flytomap apps on my device but never used the boat, now me and my mate restored the whole boat, but there is this 2 things that I'm not familiar with. I bought this fishfinder Garmin 400c, but there is plenty of cables in the back, do I need to connect them all or just the power and ground?

Should be 3 connectors: Power, transducer, and CANet. If you're not sharing data with another remote head unit, you can forget the network connector. So, as Courageous says, power and ducer.

jky

Sorry; wrong unit. One connector, bunch of cables. You need the transducer cable (with the connector) and the black and red wires conected. Yellow to a piezo transducer if you want remote audible alarms. Any unused wires should be sealed off with liquid electrical tape or adhesive-lined heatshrink tubing to prevent water ingress.